This invention relates to a valve arrangement for use in an injector arrangement.
Fuel injectors are known which are adapted to draw liquid fuel from a low pressure drain source and supply the fuel at high pressure to an outlet of the injector. Such injectors commonly have actuating means which controls a spill valve or other type of valve for controlling delivery of fuel from the injector. In this type of injector, a spill valve in axial alignment with a main fuel supply passage for supplying fuel to the injector nozzle is commonly used. Generally, the valve is either fully open, to tend to reduce the pressure in the main fuel supply passage to that of the low pressure drain, or fully closed, so as to maintain high pressure in the main fuel supply passage for injecting fuel from an injector outlet.
One problem with the above-described type of injector is that excessive pressure can be generated in the fuel-carrying passages in the injector, leading to possible structural failure of the fuel system and, in certain circumstances, the engine served by the fuel system. Another problem with the type of injector described above is that there is generally no provision for maintaining an intermediate pressure between drain pressure and pumping pressure. A particular difficulty is that, in the conventional valve arrangement, a large proportion of the actuator stroke would be taken up in moving the valve from its fully open position to the region in which it can precisely control flow to obtain a preselected intermediate pressure. For example, approximately 90% of the actuator stroke would be used to reduce the spill area sufficiently to maintain pressure at one quarter of normal supply pressure. It is difficult to control accurately the last 10% of valve travel. To maintain accuracy at the high speed required, a very large actuator would be necessary.
The invention provides a valve arrangement for an injector arrangement adapted to draw liquid fuel from a low pressure drain source and supply the fuel from a pump at high pressure through a main fuel supply passage to an outlet of the injector arrangement, the valve arrangement including pressure regulating means operable during the course of an injection to regulate the pressure of fuel being supplied to the outlet so as to provide a preselected pressure in the main fuel supply passage which is intermediate drain pressure and pump supply pressure.
Conveniently, the pressure regulating means comprises a spill valve. Using the spill valve for pressure regulating purposes obviates the requirement for separate pressure regulating means, facilitating the provision of a smaller and less complex injector arrangement.
Preferably, the pressure regulating means is operable to automatically prevent further increase of fuel pressure in the main supply passage when the pressure in that passage reaches a predetermined level.
The pressure regulating means may comprise a valve member and actuating means operable to move the valve member along an axis. The actuating means conveniently comprises a piezo electric actuator. The pressure regulating means may include auxiliary control means for co-operating with the actuating means to control the position of the valve member along the axis.
The auxiliary control means preferably uses fuel at pump supply pressure to oppose the force of the actuating means. This facilitates the provision of efficient over-pressure protection. A more linear operating characteristic is also facilitated in that valve member position is controlled using a significant portion of the stroke of the actuating means.
The axis along which the valve member is movable preferably extends laterally across the main fuel supply passage.
The valve arrangement may include a housing portion having a bore containing the valve member communicating with a larger bore containing a piston driven by an actuator, respective surfaces of the larger bore, the valve member and the piston together forming a control chamber adapted to receive fuel.
Relief means is conveniently provided, operable to direct leakage flow from the main supply passage away from the control chamber.
The valve arrangement may include cooling means operable to cool the actuator. Preferably, the cooling means circulates fuel through a chamber in which the actuator is disposed. The arrangement may be such that spill and filling pulses are utilised during operation of the injector to circulate fuel through the chamber. The invention also provides actuating means comprising an actuator for actuating a valve member in a fuel injector, the actuating means being provided with cooling means for cooling the actuator.
The invention also includes a valve arrangement for an injector arrangement adapted to draw liquid fuel from a low pressure drain source and supply the fuel from a pump at high pressure through a main fuel supply passage to an outlet of the injector arrangement, the valve arrangement including pressure regulating means operable to automatically prevent further increase of fuel pressure in the main supply passage when the pressure in that passage reaches a predetermined level.
The valve arrangement may form part of a unit pump which supplies fuel to a fuel injector through a high pressure supply passage, or may form part of the fuel injector or may form part of a unit injector in which the pump and the injector are combined in a single unit.